Biology · Introductory biology · Worked example
Identify a cell from its structures
A student observes three cells. Cell A is 2 µm long, with a cell wall, ribosomes and a ring of DNA but no nucleus. Cell B is 40 µm across, with a nucleus, a cell wall, chloroplasts and a large central vacuole. Cell C is 20 µm across, with a nucleus, mitochondria and centrioles but no cell wall. Identify each cell.
Look for a nucleus first
Cell A has no nucleus and no membrane-bound organelles, and it is only 2 µm long: it is prokaryotic, such as a bacterium. Cells B and C have nuclei, so they are eukaryotic.
Check for a wall, chloroplasts and a central vacuole
Cell B has all three, the structures that set plant cells apart from animal cells: it is a plant cell.
Check for centrioles and no wall
Cell C has centrioles, which plant cells lack, and no wall: it is an animal cell.
Check the sizes
The sizes agree: prokaryotic cells are typically 0.1–5 µm across and eukaryotic cells 10–100 µm. Cell B is 20 times as long as cell A.
Result
Cell A is prokaryotic, such as a bacterium; cell B is a plant cell; cell C is an animal cell.
Your turn
A cell 15 µm across has a nucleus, mitochondria and chloroplasts. Is it prokaryotic or eukaryotic, and is it more likely a plant cell or an animal cell?
Show the answer and explanation
Eukaryotic, and a plant cell, or another photosynthetic eukaryote such as an alga.
The nucleus makes it eukaryotic, and chloroplasts occur in plants and algae, never in animal cells.
Keep exploring
The plant cell opens in Biology with its organelles drawn and labelled.
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Open the plant cell Open worked example on a board Cell structures in Biology ReferenceYour existing work stays on this device. Examples open as editable copies.